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From Bruno René Santos <brunor...@holos.pt>
Subject Re: Querying on Inherited Objects
Date Wed, 09 Mar 2011 12:29:53 GMT
Hi Marcin,

What you said makes sense. When i query for a parent I will get all 
children also. At this moment I solved the problem by using two distinct 
ObjEntities that point to a single DBEntity. Its working

Thanx a lot
Bruno

Em 07-03-2011 22:24, Marcin Skladaniec escreveu:
> Hi Bruno
>
> All squares are rectangles, but some rectangles are squares, the query 
> for rectangles will also give you squares. This is a valid result from 
> cayenne's perspective.
>
> What you looking for is to query for Rectangle but not Square. I see 
> three ways of doing that:
> - query for Parent, query for Child, subtract results from each other. 
> (performQuery(Rectangle).removeAll(performQuery(Square))
> - create another subclass of Parent, mutually exclusive with Child, 
> and query that. (performQuery(NotSquare))
> - expose the qualifier field in cayenne modeler, query with the 
> qualifier. (performQuery(Rectangle, 
> ExpressionFactory.noMatch(polygonType, square))
>
>
> With regards
> Marcin
>
>
>
> On 6/03/11 11:18 PM, Bruno René Santos wrote:
>> Both parent and child are the same on the database level. But each 
>> object is used differently on the GUI level. As both GUIs must 
>> cohexist temporarily I thought I could do a child object from the 
>> current used object and change some logic on it. So i got something 
>> like this
>>
>> Child extends _Child
>>
>> _Child extends Parent
>>
>> Parent extends _Parent
>>
>> _Parent extends CayenneDataObject
>>
>> The only issue here (at least I think...) is that a performQuery(new 
>> SelectQuery(Child.class)) will correctly return a list of Child but a 
>> performQuery(new SelectQuery(Parent.class)) will also return a List 
>> of Child... Any way to return a List of Parent?
>>
>> Thanx
>> Bruno
>>
>> Em 06-03-2011 10:15, Aristedes Maniatis escreveu:
>>> On 6/03/11 9:03 PM, Bruno René Santos wrote:
>>>> I have an object structure with a Child dataobject which inherits 
>>>> from a Parent which is linked to a db_entity. I am trying to use 
>>>> the Parent on a GUI and the Child on another GUI. The Child 
>>>> overrides some methods from the Parent (but the db table is the 
>>>> same) and so is mandatory that on each GUI their respective 
>>>> searches yeld Child objects or Parent objects. On the GUI that uses 
>>>> the Child everything goes according plan, the performQueries return 
>>>> lists of Children. But on the Parent GUI I call
>>>>
>>>> context.performQuery(new SelectQuery(Parent.class))
>>>>
>>>> but the method returns also a list of Children, which are 
>>>> incompatible with the parent GUI. Is there any way that this query 
>>>> returns Parents instead of Children? I was trying these inheritance 
>>>> so that i could reuse all db fields and relationships from the 
>>>> parent on the child.
>>>
>>> What does the discriminator column say about these objects? Are they 
>>> actually Child entities in the database or Parent? They can't be 
>>> both at the same time.
>>>
>>> This isn't like plain-old Java inheritance where you can just cast 
>>> from one to the other as needed. If you could, what would happen if 
>>> you queried for a list of Child objects, casting them as Parents, 
>>> changed some Parent attribute and committed the context? Would they 
>>> now become Parents in the database?
>>>
>>> Ari
>>>
>>>
>>
>>
>
>
>
>


-- 
Bruno René Santos | brunorene@holos.pt <mailto:brunorene@holos.pt> | 
Gestor de Projectos | Analista | Programador | Investigador

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